This proposal is designed to examine the role of RII beta knockout mice demonstrate a lean phenotype which correlates with the type II to type I isotype switch that is observed in brown and white fat. Since RIIbeta is also expressed in brain, we propose to determine which tissue is responsible for the development of the lean phenotype. To achieve this we will use a novel genetic approach to generate mice that express RII(3 only in brown fat. Our prediction is that these mice will be rescued from the mutant "lean" phenotype. Our strategy requires generating two strains of mice and combines use of homologous and Cre-lox-mediated recombination. In one strain, wildtype RII beta expression is inactivated in all tissues by introduction of a marker gene (flanked by lox sites) that disrupts gene expression. In the second strain, transgenic mice selectively express Cre recombinase in brown fat using the uncoupling protein promoter. When these two mouse strains are crossed, their progeny should only express RII beta in brown fat after Cre recombinase excises the disrupting marker gene. A similar strategy will also be used to examine the importance of subcellular localization of RII beta/PKA. In this case we will replace wild type RII(3 expression in all tissues with an anchoring-deficient mutant. The mutant contains two amino acid point mutations in the N-terminus of RIIbeta that are known to disrupt RII associations with A kinase anchoring proteins (AKAPs). If anchoring of RII beta in fat is essential for the regulation of body fat content, future identification of adipose specific AKAPs could point to new leads for therapeutic interventions in the treatment of obesity.